1. Field of the Invention
This invention relates to a solid-state electronic image sensing device, an image sensing apparatus and methods of controlling operation of the device and apparatus.
2. Description of the Related Art
A solid-state electronic image sensor such as a CCD is utilized as the image sensor in a digital still camera. An increase in the number of pixels used in solid-state electronic image sensors has been accompanied by the need for a longer period of time to obtain output of a video signal from the image sensor.
In a digital still camera, angle-of-view adjustments and the like can be made so long as the subject can be checked in general. This means that a video signal corresponding to all pixels capable of being output by the solid-state electronic image sensor is not necessarily required. For this reason, there are instances where line downsampling is performed in such a manner that only one row (line) of a video signal is output for every plurality of rows in the vertical direction of the solid-state electronic image sensor. Since this approache reduces the amount of video signal output from the solid-state electronic image sensor, output of the video signal ends in a short period of time.
At certain times, such as when the subject is brightly illuminated, signal charge that has accumulated in photodiodes of a solid-state electronic image sensor leaks into adjacent photodiodes or into the vertical transfer lines, etc., as a result of which a phenomenon referred to as smear occurs. Even if line downsampling is performed, unnecessary signal charge that has leaked from the photodiodes of a row to be downsampled leaks into the vertical transfer lines and is superimposed upon the video signal to be output. This causes a decline in image quality.
In general, color filters are formed on the photodiodes of a solid-state electronic image sensor so that an RGB color video signal can be output. The RGB color video signal output from the solid-state electronic image sensor is separated color by color to produce luminance data and color difference data, etc. It is preferred, therefore, that a video signal that has already been separated into its individual colors be output at the moment an output is produced by the solid-state electronic image sensor.
Accordingly, an object of the present invention is to prevent a decline in image quality due to smear even if line downsampling is performed.
Another object of the present invention is to utilize unnecessary signal charge effectively.
A further object of the present invention is to so arrange it that a solid-state electronic image sensor can output a video signal that has been separated color by color.
According to a first aspect of the present invention, the foregoing objects are attained by providing a solid-state electronic image sensing device comprising: a number of photoelectric transducers arrayed in vertical and horizontal directions; vertical transfer lines, on which vertical transfer electrodes are formed in correspondence with the photoelectric transducers, for transferring signal charge, which has accumulated in the photoelectric transducers, in the vertical direction by application of vertical transfer pulses to the vertical transfer electrodes; a horizontal transfer line for transferring in the horizontal direction and outputting signal charge that has been transferred from the vertical transfer lines; a charge sweep-out drain for sweeping out signal charge input thereto; and a controller which, when vertical downsampling readout is performed, is for controlling the vertical transfer lines and the horizontal transfer line in such a manner that of signal charge that has accumulated in a plurality of rows of the photoelectric transducers, signal charge that has accumulated in at least one row of these photoelectric transducers is output from the horizontal transfer line, and controlling the vertical transfer lines and the horizontal transfer line in such a manner that smear charge, which is produced in vertical transfer lines between the vertical transfer electrodes corresponding to the photoelectric transducers of the one row, is applied to the charge sweep-out drain and is swept out from the charge sweep-out drain.
The first aspect of the present invention also provides a control method suited to the above-described solid-state electronic image sensing device. Specifically, there is provided a method of controlling a solid-state electronic image sensing device having a number of photoelectric transducers arrayed in vertical and horizontal directions; vertical transfer lines, on which vertical transfer electrodes are formed in correspondence with said photoelectric transducers, for transferring signal charge, which has accumulated in said photoelectric transducers, in the vertical direction by application of vertical transfer pulses to the vertical transfer electrodes, and a horizontal transfer line for transferring in the horizontal direction and outputting signal charge that has been transferred from the vertical transfer lines; the method comprising the steps of: providing a charge sweep-out drain for sweeping out signal charge input thereto; and when vertical downsampling readout is performed, controlling the vertical transfer lines and the horizontal transfer line in such a manner that of signal charge that has accumulated in a plurality of rows of the photoelectric transducers, signal charge that has accumulated in at least one row of these photoelectric transducers is output from the horizontal transfer line, and controlling the vertical transfer lines and the horizontal transfer line in such a manner that smear charge, which is produced in vertical transfer lines between the vertical transfer electrodes corresponding to the photoelectric transducer of the one row, is applied to the charge sweep-out drain and is swept out from the charge sweep-out drain.
In accordance with the first aspect of the present invention, the charge sweep-out drain is provided.
When vertical downsampling readout is performed, signal charge, which has accumulated in at least one row of photoelectric transducers, of signal charge accumulated in photoelectric transducers of a plurality of rows is output from the horizontal transfer line as a video signal. Smear charge, which is produced in vertical transfer lines between the vertical transfer electrodes corresponding to the photoelectric transducers of the one row, is swept out from the charge sweep-out drain.
Thus, smear charge is swept out from the sweep-out drain and does not become superimposed on the video signal that is output from the horizontal transfer lines. This makes it possible to prevent a decline in image quality caused by superposition of smear charge on the video signal.
The control unit may be so adapted that when vertical downsampling readout is performed, the control unit controls the vertical transfer lines and the horizontal transfer line in such a manner that of signal charge that has accumulated in three or more rows of the photoelectric transducers, signal charge that has accumulated in at least one row of these photoelectric transducers is output from the horizontal transfer line, and controls the vertical transfer lines and the horizontal transfer line in such a manner that smear charge of a plurality of rows, which is produced in vertical transfer lines between the vertical transfer electrodes corresponding to the photoelectric transducers of the one row, is accumulated temporarily in the horizontal transfer line and the accumulated smear charge of the plurality of rows is swept out from the charge sweep-out drain.
Thus, smear charge of a plurality of rows can be accumulated temporarily in the charge sweep-out drain and then this charge can be swept out collectively thereafter.
According to a second aspect of the present invention, the foregoing objects are attained by providing an image sensing apparatus comprising: an image sensing device for sensing the image of a subject, and outputting a video signal representing the image of the subject, using a solid-state electronic image sensing device having vertical transfer lines on which vertical transfer electrodes are formed in correspondence with a number of photoelectric transducers arrayed in vertical and horizontal directions, a horizontal transfer line for transferring in the horizontal direction and outputting signal charge that has been transferred from the vertical transfer lines, a charge sweep-out drain for sweeping out signal charge input thereto, and a device which, when vertical downsampling readout is performed, is for controlling the vertical transfer lines and the horizontal transfer line in such a manner that signal charge that has accumulated in at least one row of the photoelectric transducers among a plurality of rows thereof is output from the horizontal transfer line as a video signal, and in such a manner that signal charge that has accumulated in the photoelectric transducers of the one row is applied to the charge sweep-out drain and is swept out from the charge sweep-out drain; an exposure controller for controlling exposure of the photoelectric transducers of the solid-state electronic image sensing device in accordance with an applied exposure control signal; and an exposure-amount calculator for calculating amount of exposure based upon signal charge that has been swept out from the charge sweep-out drain, generating the exposure control signal in such a manner that the amount of exposure becomes the calculated amount of exposure, and applying the exposure control signal to the exposure controller.
The second aspect of the present invention also provides a control method suited to the above-described image sensing apparatus. Specifically, there is provided a method of controlling an image sensing apparatus comprising the steps of: obtaining a video signal representing the image of a subject by sensing the image of the subject using a solid-state electronic image sensing device having vertical transfer lines on which vertical transfer electrodes are formed in correspondence with a number of photoelectric transducers arrayed in vertical and horizontal directions, a horizontal transfer line for transferring in the horizontal direction and outputting signal charge that has been transferred from the vertical transfer lines, a charge sweep-out drain for sweeping out signal charge input thereto, and a device which, when vertical downsampling readout is performed, is for controlling the vertical transfer lines and the horizontal transfer line in such a manner that signal charge that has accumulated in at least one row of the photoelectric transducers among a plurality of rows thereof is output from the horizontal transfer line as a video signal, and in such a manner that signal charge that has accumulated in the photoelectric transducers of the one row is applied to the charge sweep-out drain and is swept out from the charge sweep-out drain; calculating amount of exposure based upon signal charge that has been swept out from the charge sweep-out drain; and controlling exposure of the photoelectric transducers in such a manner that the amount of exposure becomes the calculated amount of exposure.
In accordance with the second aspect of the present invention, amount of exposure is calculated using signal charge that has accumulated in the photoelectric transducers of a line to be downsampled, and exposure control is then executed. The signal charge is swept out independently of the video signal output from the horizontal transfer line. As a result, exposure control can be executed using signal charge while the image represented by the video signal output from the horizontal transfer line is displayed.
According to a third aspect of the present invention, the foregoing objects are attained by providing a solid-state electronic image sensing device comprising: a number of photoelectric transducers arrayed in vertical and horizontal directions; a color filter formed on each of the photoelectric transducers and having a characteristic that allows transmission of a red, blue or green color component; vertical transfer lines for transferring signal charge, which has accumulated in the photoelectric transducers, in the vertical direction; a horizontal transfer line for temporarily accumulating signal charge that has been transferred from the vertical transfer lines, and transferring the signal charge in the horizontal direction; a charge sweep-out drain for sweeping out signal charge input thereto; and a transfer gate for transferring the signal charge, which has accumulated temporarily in the horizontal transfer line, from the horizontal transfer line to the charge sweep-out drain on a per-red-color-, blue-color- or green-color-component basis.
The third aspect of the present invention also provides a control method suited to the above-described solid-state electronic image sensing device. Specifically, there is provided a method of controlling a solid-state electronic image sensing device having a number of photoelectric transducers arrayed in vertical and horizontal directions, a color filter formed on each of the photoelectric transducers and having a characteristic that allows transmission of a red, blue or green color component, vertical transfer lines for transferring signal charge, which has accumulated in the photoelectric transducers, in the vertical direction, and a horizontal transfer line for temporarily accumulating signal charge that has been transferred from the vertical transfer lines, and transferring the signal charge in the horizontal direction, the method comprising the steps of: providing a charge sweep-out drain for sweeping out signal charge input thereto; and transferring the signal charge, which has accumulated temporarily in the horizontal transfer line, from the horizontal transfer line to the charge sweep-out drain on a per-red-color-, blue-color- or green-color-component basis.
In accordance with the third aspect of the present invention, the charge sweep-out drain is provided. Signal charge is accumulated temporarily in the horizontal transfer line. Of the temporarily accumulated signal charge, charge is transferred from the horizontal transfer line to the charge sweep-out drain on a per-red-color-, blue-color- or green-color-component basis. Signal charge of each of a red, blue or green color component is transferred from the charge sweep-out drain and output.
Thus, signal charge of each of a red, blue or green color component is obtained.
Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof.